1. Field of Invention
The present invention relates to a low pressure exhaust gas recirculation (EGR) system and a control method thereof. More particularly, the present invention relates to a low pressure EGR system that prevents reverse flow of exhaust gas recirculated to the engine, and a control method thereof.
2. Description of Related Art
Generally, an exhaust gas recirculation system is disposed in an engine to recirculate the exhaust gas to an intake line such that the combustion temperature is decreased to suppress NOx generation.
A target air amount is set according to an operating area of an engine, and an EGR duty ratio is controlled to adjust an EGR gas amount and fresh intake air. The EGR gas amount (flow rate) is set to correspond to the operating area beforehand, and the operating area of the engine is determined to control the EGR valve such that the exhaust gas flow rate (amount) is adjusted.
Particularly, a diesel engine is provided with a turbocharger, which uses energy of the exhaust gas to compress intake air such that the charging efficiency of the air is improved, the engine output is increased, the emission quality is stable, and the fuel efficiency is enhanced.
Also, a low pressure EGR system has been developed so as to reduce emission generation, wherein fresh air is not supplied to the engine and the fresh intake air and the exhaust gas can flow backward to the low pressure EGR line if a high pressure is formed around a join portion where the intake air and the recirculated exhaust gas join together. If the recirculated exhaust gas flows in a counter direction through the low pressure EGR line, the low pressure EGR system cannot reduce the NOx or improve the fuel consumption efficiency.
Accordingly, it is necessary to determine whether the recirculated exhaust gas flows backward in the low pressure EGR line.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.